Circuit protective device



1952 G. v. ZlTO 2,615,107

CIRCUIT PROTECTIVE DEVICE Filed Sept. 29, 1949 FIG. 1

IN V EN TOR.

GEORGE 1! 2/70 Patented Oct. 21, 1952 UNITED STATES. PATENT OFFICE i I 2,615,107 CIRCUIT PROTECTIVE DEVICE George V. Zito, Jersey City, N. J.,'assignor: to

BendixAviation Corporation, Teterboro, N. J.,

a. corporation of Delaware t Application September 29, 1949, Serial No. 118,635

The present invention relates to protective means such as fuses or the like for an electrical circuit; 1

The invention finds particular utility in control applications employing a sensing element, wherein an open circuit condition due to failure, corrosion, or'otherwise destructive features subjects the system to an immediate loss of control, and 'in aircraft applications where due to the inherent ruggedness of the device, possibility of vibration failure is minimized.

One such sensing element and embodying circuitis illustrated in copending application Serial No. 63,381 on Temperature Probe, filed December 3, 1948 in the name of William R. Polye and assigned to Bendix Aviation Corporation.

The present invention contemplates the immediate removal of the erroneous signal and substitution therefor of a standby device or resistance of the same value sothat the circuit as a whole remains balanced.

"Heretofore in such safety circuits it has been common in the art to employ a latching type relay, however, 'said type of protective device has proven'maladjustedin circuits involving low power applications,'due to-the loss of sensitivity of the relay in overcoming the mechanical inertia of the latch. M

It is, therefore, one of the objects of the invention to provide control circuit protective means wherein the foregoing disadvantage is eliminated; and to do so in a novel and effective manner.

- Another-object of the invention is to provide a circuit protective device which will permit auxiliary control, or give indication of failure of some electrical device.

Still another object of the invention is to provide a fuse,"or circuit safety device of the aboveindicatedcharacter which will function. effectively in circuits wherein low power is involved.

Still another object of the inventio n is to provide a fuse for an electrical circuit which dispenses with the use of solder or other fusible means. i

Still another object of theinventi'on is to provide a protective device of theiabove-indica'ted nature which shall be light, yet extremely rugged and durable, and impervious to the vibrational stresses encountered in aircraft installations.

, Another object of the, invention is to provide control circuit protective. means which are con},

nected in parallel-rather than in series with the circuit load. I

Still another object of the invention is to pro- 5 Claims. (01. 200-122 vide a fuse fulfilling the above objects which shall be simple and economical to manufacture and positive and reliable in operation.

' The foregoing and manifold and multiple other objects and advantages shall become increasingly manifest upon a consideration of the subsequent description and accompanying drawing, wherein one embodiment of the invention is illustrated "by way of example. It is expressly understood, however, that the drawing serves the purpose of illustration only, and is not to be construed as defining the limits of the invention.

In the drawing: 7 Figure l is an elevational view construction of the'fuse.

Figure 2 is a wiring diagramillustrating the embodiment of the invention,

Referring now to the drawing, and more particularly to Figure 1, the-fuse generally designated by the numeral [0 comprises a length of gla'ss'tubing l2 and terminal caps M and IE on each end thereof. The terminal can I4 has attached to its inner surface, as by rivet ill, a con tact 20, while the cap [6 has affixed thereto a washer ring 22 of'brass or some similar conductive material, insulated therefrom by means of a fiber ring 24. A through hole 26 in the rings 22 and 24 communicates thro'ugha concentric hole 28 of larger diameter in the cap l6, with the interior of the fuse l0.

A second contact 30 is affixed toone end of'acompression spring 32, while the other end of the spring 32 is anchored a-gainst the' terminal cap I6. 'The'spring 32 is under compression and tends to bias the contact 30 to make junction} with the contact-'20, 'but is restrained from. so

doing by a strand assembly generally designated as 34 which issecured atone endto the contact 30, and at the other end, as by solder means to mar e 22.

The'strand assembly 34 is composed of a length 36 of strong cotton, linen or laniferous fiber impregnated in a solution of some highly inflammable' and combustible reagent such as sodium ance wire 38 is entwined about the 'material't fi and attached to nickel terminal 40 through holes 26 and 28, "Another nickel tab 42 serves as a means'for soldering the contact 30 to'the strand assembly 34, including the opposite end of" the high resistance wire 38. The contact'iifl is mam connected through the cap [6.

Referr ing' now to EigureZ fOr-an application of the device, a bridgeM-comprising resistors showing the A winding of high resistspring 32 to the terminal 46, 48, 50 and 52 is fed from a source of electrical potential 54.

The resistance 46 is a sensing device such as, for example, a high temperature probe, and the signal voltage from the bridge, herein designated as Es is proportional to the resistive change of the sensing device.

An identical standby sensing device 56, or a resistance of the same value as that of device 46 is in readiness to be connected into the circuit by contact 30 in the event of failure or shunting out of the element 46.

Having thus described the invention, it will now be apparent to those skilled in the art that when a voltage as from source 54 is applied across the bridge, it will divide itself across the resistances 46 and 52 in proportion to their respective values. Upon an open circuit condition of the sensing element 46, however, the full bridge voltage will be applied instantaneously through the high, resistance wire 38, wrapped around the strand assembly. 34.

Thereupon the high resistance wire 38,will heat rapidly and ignite. the sodium nitrate saturated strand assembly 34-, thereby causing it to break and relieve the compression of the spring 32,-. The contacts 20' and 30; will then be sprung shut, thereby connecting the standby elementor resist ance 5,6 in place of the open circuited element 4.6. The resistance 36 remains in the circuit asbefore, therefore, calibration. of the circuit remains unaltered.

It is to be noted that when the value of the resistance 46 is. oi low O iQOrder, the extremely high resistance wire 38 in parallel therewith draws only a negligible current,

There are thus provided control circuit protection means whereby an erroneous signal is immediately corrected by substitution of a standby signaling device. Further provided are positive and reliable fuse means which are rugged and durable, simple and economical to manufacture, and which dispense with the usual. fusible element.

Although only one embodiment and-one application of the invention has, been illustrated and described, other changes and modifications in the form and relative arrangement of parts which will be apparent to those skilled in the art may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a circuit protective device, the combinationcomprising a glass, tubing, a first metal can and a, second metal cap closing each end, of said tubing, a contact inside said tube attached to said first cap, a compressionv spring anchored to said second cap, a mating contact attached to the endof said spring, a combustible fiber strand assembly attached to the exterior of said second cap restraining said spring, said strand assembly being impregnated. with sodium nitrate, a. high resistance wire encircling said strand assembly adapted upon excessive current passing therethrough to. ignite said impregnated strand assembly thereby freeing said spring to join said contacts.

2. In a circuit protective device, the combination comprising a tube, a cap closing each end of said tube, an open. electrical contact within said tube, spring means biasing said contact towards closed position, an inflammable strand assembly restraining said spring, a resistance wire entwined, about said strand assembly adapted upon overheating thereof to ignite said strand assem- 4 Elytthereby freeing said spring to close said con- 3. A circuit protective device comprising, in combination, a tube, a terminal cap for each end of said tube including a relay contact on one of said caps, a second relay contact within said tube, spring means biasing said second contact towards said first contact and terminal cap, an inflammable strand restraining said spring means, a resistance wire entwining said strand adapted upon overheating to ignite said strand thereby permitting said spring to join said contacts, said spring completing contact between said terminal caps.

4. A circuit protective device for use in closing a, circuit while maintaining a first established circuit, comprising a tube made of insulating material, a first conductive cap closing one end of said tube, a second conductive cap closing the opposite end of said tube, a first electrical contact attached to said first. cap and positioned withinsaid tube, a conductive compressionspring positioned within said tube and attached at one end thereof to said second cap, a. second electrical contact carried by the other end. of said spring, a terminal, conductive plate carried by and insulated from, said second. cap, a combustible fiber strand assembly attached. to said terminal plate and operative to restrain said spring;

a high resistance wire helically wound. around the strand assembly, said resistance wire being connected between said second electrical contact and said conductive plate to provide a first electrical circuit from said terminal plate to said second cap, said strand assembly beingv adaptzd to ignite upon excessive current overheating; said resistance wire to thereby release said spring, whereby said first and second electrical contacts are joined toclose a second electrical circuit be: tween said first and second caps, and; said re.- sistance wire being of sufiicient length to accommodate the expansion of said spring, to permit the maintenance of said first circuit.

5. A circuit protective device for use inclosing;

a circuit while maintaining a. first established circuit, comprising afirst electrical terminal, a-

first contact mounted on said first terminal, a. second electrical terminal, a conductive compress sion spring mounted on said second terminal, a second contact carried by said spring and ens gageable with said first contact upon the ex,- pansion of said spring to close-an electricaleib cuit between said first and second terminals, a third electrical terminal, restraining meansim eluding an inflammable element and operativebetween said. second contact and third, terminal,

to maintain said spring in compression and said first and second, contacts out of engagement, a

resistance wire helically wound aroundsaid inflammable element and electrically connected; to-

said third terminal and through said second contact and spring to said second terminal'to providea first electrical circuit, said resistance alemerit upon passage of excess current; there? through being operative to overheat so as to cause said inflammable element. to ignite and thereby releasing said spring to permit the engagement of said first; and-second contacts toclose a. second electrical circuit between said first. and second terminals, and saidresistance ele ment being so constructed and. arranged as to permit maintenance of saidfirst circuit upon the closing of the second circuit'aforesaid;

GEORGE V. ZITO.

(References on following page) 6 REFERENCES CITED Number Name Date The following references are of record in the 13809 Wefel 8, 1918 file of patent: pp ug- 1,935,611 Bourbon Nov. 21, 1933 UNITED STATES PATENTS 5 1,966,120 Gross July 10, 1934 Number Name Date 1,966,466 Smalley July 17, 1934 689,817 Hansen et a1. Dec. 24, 1901 2,302,086 Zierdt, Jr Nov. 1'7, 1942 1,239,140 Torchio Sept. 4, 1917 

